To meet the demands of the construction industries, hardwood forests have been depleted steadily, since a large number of structural elements, e.g., railway ties, telephone poles, guard rails, fences and decks have been constructed of such hardwoods. Many industrialized countries have attempted to conserve such forests by developing recycling programs to reduce the need for cutting down trees and to provide a sufficient amount of timber suitable for use in construction. Such recycled timber typically needs to be chemically treated before use for biological resistance and/or strengthening, and thus tends to be rendered toxic.
Railway ties, which are used to support railway tracks on a roadbed of ballast or concrete, are typically made of wood. Wood is the generally preferred constituent material because it can withstand climatic changes, and wooden ties are relatively easy to install and replace. Since thousands of miles of railway tracks are in use throughout the world, a vast number of railway ties is needed each year to replace those which have been worn out over time.
Although wooden railway ties provide durability and withstand well the static and dynamic loads of freight and passenger trains, they are susceptible to attack from fungi and insects which will weaken and eventually deteriorate the railway ties. The lifespan of wooden railway ties can be prolonged by the use of preservatives, in particular creosote, but such preservatives result in potential environmental hazards, both during the treatment procedure for the manufacture of ties, and by reason of leaching of creosote into the surrounding soil and the water table in the region of the railroad. Further, railway ties which have been chemically-treated present a disposal problem in view of environmental concerns over the hazardous chemical preservatives.
Notwithstanding their relative ability to withstand the North American climate, wooden railway ties are susceptible to damage from harsh weather conditions and excessive sunlight. Consequently, they require frequent monitoring and maintenance to prevent failure due to splits (separation along the grain) deterioration of fastening device anchorage, decay and warps. Thus the cost of maintenance of such wooden railway ties can be substantial.
Concrete railway ties are popular in Europe and in Japan, where the availability of hardwood for railway ties is limited. However concrete railway ties, too, have several disadvantages. They are relatively expensive and can crack or spall over a number of years, particularly where used in areas subject to dramatic climactic changes. More significantly, they are susceptible to erosion under the load of rolling stock.
Steel railway ties have also been proposed and put into use, however, they have proved disappointing, since they are susceptible to rust and fatigue factors, and generate an unacceptable high noise level during use. Steel railway ties are more susceptible than wooden ties to shifting within the ballast. Moreover, in those installations in which the steel railway rails are used to send electrical signals along the railroad right-of-way, and must therefore be electrically isolated from one another, the use of electrically-conductive steel railway ties between the rails requires expensive additional insulation.